Anti-reflective (AR) coatings are used in several industries, including in the manufacture of photovoltaic (PV) modules, to reduce the reflection fraction of incident light as light passes through an optically transparent element such as glass. The goal of AR coatings is to achieve a refractive index that is as close to 1.23 as possible to maximize light transmission over a broad band of light wavelengths.
One or more layers of a low refractive index coating can achieve improved transmittance in a broad wavelength range and a wide range of incident angles. Such coatings can be deposited (at atmospheric pressure or without vacuum) as sol-gel materials and can be highly cost-effective. These thin anti-reflective coatings, which may be formed from a silicon dioxide sol-gel applied to the glass cover by conventional coating techniques, have been reported to improve solar light transmittance by about two to three percent in the visible portion of the light spectrum. Such sol-gels have been formed using several mechanisms including via hydrolysis/condensation reaction of alkoxy silanes. See, e.g., G. Wu et al., “A novel route to control refractive index of sol-gel derived nanoporous films used as broadband antireflective coatings,” Materials Science and Engineering B78 (2000), pp. 135-139. However, AR coatings formed from silicon dioxide coatings would benefit from improved hardness, adhesion, shelf-life and/or processing efficiency.